This invention relates to a method of and means for separating oil from water in order to allow substantially oil-free discharge of water into streams or bays. In particular, the invention relates to a separator-filter combination which is adaptable for use in small boats, harbor craft, ships, or shore installations.
Concern over the purity of water in harbors and streams has recently resulted in extremely rigid standards for discharge of waste fluids into such streams. These standards are applicable both to waterborne installations and to shore establishments. In the waterborne environment, particularly with small harbor craft, a continuing problem of maintaining a dry bilge imposes a hardship on the operator if he must place his money producing craft alongside a particularly designed pier every time it is necessary to pump bilges. It is an inherent characteristic of such waterborne craft that not only does water accumulate in the bilges, but fuel and lubricating oil is almost always present in the bilges. In addition to the residue from operating internal combustion engines which usually power small watercraft, an oil spill in the bilges is not uncommon. In ships where steam may be the primary means for providing propulsion, oil is also present in the bilges. Such oil from steam plants, of course, comes from the same source, i.e., lubrication or the fuel utilized in the boiler to generate the steam.
Pumping of bilges is an absolute necessity in any waterborne craft or ship. To leave free liquid in the bilges has a detrimental effect on the stability of the ship. It is well known that the larger the free surface of water in a ship's compartment, the greater the instability that free surface imparts to the ship. It is also well known that free liquid in the bilges adversely affects the metacentric height or righting moment of the ship. In addition to the stability problem which is of vital importance at any time in a ship or watercraft, the accumulation of liquid, particularly water, in a steel hulled or a wooden hulled ship can cause corrosion or dry rot if allowed to remain. Finally, the oil, which as noted above is almost endemic in bilges, is an ever present fire hazard.
Having presented the problem of the boat owner, it is appropriate to present the problem of the environmentalist. For years, boat owners and ship owners have solved the problem of removing bilge water from the hull by pumping the residue over the side and letting nature take its course in breaking down the oil and other contaminants that was present in the effluent. It is unnecessary to elaborate on recent changes in the attitude of the public and consequently, the government, toward the environmental standards for streams and bodies of water. The standards specify the effluent pumped from a ship leave the water surrounding the ship "sheen free" and further cause no discoloration below the surface of the water. It is immediately apparent to those skilled in the art that pumping any bilge water over the side immediately runs the risk of violating these rather stringent standards. In summary, what must be accomplished is that all solids must be removed from the bilge water before discharge, all agents which discolor the water must be removed from the water, and finally, all oil or hydrocarbon content must be removed from the water.
Limiting factors in designing a system to accomplish the above objects of providing a means to effectively remove hydrocarbons and other contaminants from the oily bilge water in a small waterborne craft include size and weight. In commercial craft, such as fishing vessels, size and weight becomes particularly important as additional weight added to the craft or space used by machinery is weight and space that is effectively lost to dollar producing cargo. Another limiting factor is the capacity of the pump. Such a pump must have sufficient capacity to empty the bilges in a reasonable period of time. Furthermore, a bilge pump may in certain circumstances be utilized to dewater the hull of a vessel that has been holed in an accident. Ideally, one would like a high capacity pump which is lightweight and takes up a small amount of space. Unfortunately, high capacity pumps have a tendency to emulsify oil and water to the point where separation of the oil and water becomes difficult. Furthermore, a filter system which is capable of handling the output of a high capacity pump must of necessity be very large. Therefore, it becomes necessary to compromise between the size and weight constraints dictated by small water craft and the capacity of the system.
One other problem associated with an oily water separator of the type envisioned is the ability to discharge large amounts of oil-free water while retaining the separated oil and contaminants on board. Thus, it is necessary to provide for extraction of the separated oil from the separator and for communication of that oil to a holding tank in order not to exceed the storage capacity of the separator.
Accordingly, this invention provides an oily water separator, which may include a prefilter to remove particulate matter greater than a predetermined size, comprising a separator which removes bulk oil from the oily water stream. After bulk oil is removed from the stream, the almost oil-free water is pumped through coalescing elements and finally through a finish or polish filter to remove essentially all remaining hydrocarbon residue leaving sheen free and uncolored effluent for discharge. The system may also include automatic sensing elements to reverse the flow of the pump which, in combination with check valves in the system, allow for communication of accumulated oil in the separator to a holding tank. Normal pump flow may be automatically restored when the accumulated oil has been removed from the separator. The oily water separator may be limited in size to make it adaptable for use in small craft.